During progesterone-stimulated Xenopus oocyte maturation, certain pre-existing (maternal) mRNAs are selectively translated in a strict temporal order. The early translational activation of the Mos mRNA requires a Musashi binding element (MBE) that is located in the Mos 3’ untranslated region (UTR). The MBE lies within a 24 nt region originally termed a polyadenylation response element (PRE), but further analyses demonstrated that the MBE within this sequence was critical for temporal regul......